The present invention generally relates to printer apparatus and methods and more particularly relates to a printer and receiver supply tray adapted to sense amount of receiver therein, and method thereof.
Thermal printers form a color print by successively printing with a dye donor onto individual sheets of a dye receiver (i.e., paper or transparency). The print head of such a thermal printer commonly provides a print line of thermal resistive elements that can be individually heated in order to transfer dye from the donor to the receiver. Such print heads can take any of several forms including resistive element, resistive ribbon and laser print heads.
More specifically, a typical color thermal printer includes the previously mentioned print head and a platen. A picker mechanism "picks" individual sheets of the receiver from a stack of cut sheets of the receiver and feeds the individual sheets into a nip area defined between the print head and platen. The donor is positioned between the print head and platen. The print head is then lowered, so that the donor and receiver sheet are sandwiched between the print head and platen. An image is printed on the sheet by selectively heating the elements of the print head in order to transfer a first dye to the receiver sheet. The receiver sheet is then repositioned to receive a second color of the image, and the donor is positioned to provide a second dye color. These steps are repeated until all colors of the image are printed and the completed print is ejected from the printer.
Moreover, a receiver cassette tray loaded with the stack of cut receiver sheets is removably inserted into the printer. However, the height of the tray is usually limited in order to reduce the overall height of the printer, so that the printer may fit within confined spaces, such as are found in shelving and equipment racks. However, limiting height of the tray also limits number of receiver sheets that can be stored in the tray. This limitation in number of receiver sheets in turn causes the printer to run-out of sheets relatively quickly, thereby necessitating frequent replenishment of receiver sheets. However, it is inconvenient for the printer to run-out of receiver sheets during a production run, which may occur if the tray is low in receiver sheets at the start of the production run. It is therefore desirable to avoid starting a production run when the number of sheets in the tray is low. Therefore, the prior art printers mentioned hereinabove suffer from a problem of running-out of receiver sheets during a production run due to low receiver sheets being present in the tray at the start of the production run.
In addition, the receiver tray may include a cardboard plaque at the bottom of the stack of receiver sheets for supporting the stack of receiver sheets. When the stack of receiver sheets is depleted, the previously mentioned picker attempts to "pick" the cardboard plaque; however, the picker cannot pick the cardboard plaque due to the weight and stiffness of the cardboard plaque. When this occurs, some printers generate an error code shown on a display attached to the printer, which error code erroneously informs an operator of the printer that the printer has malfunctioned and is unable to pick receiver sheets. It is desirable to avoid display of the error code, which occurs when the picker attempts to pick the cardboard plaque. Therefore, another problem in the art is generation of an error code due to the picker attempting to pick the cardboard plaque at the bottom of a stack of receiver sheets.
Printers having low paper detection systems are known. An image production device having a paper supply "low" detection system is disclosed in U.S. Pat. No. 5,629,672 titled "Low Paper Detection System" issued May 13, 1997 in the name of Stephen S. Brown, et al. This patent discloses a paper image reproduction device having a cabinet which in turn has at least one paper cassette therein bearing a supply of stacked paper sheets. A detector is disposed in the cabinet for sensing a partial supply of paper in the paper cassette. However, the Brown et al. disclosure requires use of a cabinet in addition to the paper cassette. This cabinet is an additional bulky component that must be inserted into the printer. This is undesirable because use of an additional bulky component increases cost of the printer and may decrease printer reliability. Also, use of such an additional major component necessarily increases the "footprint" or even height of the printer. Therefore, yet another problem in the art is addition of a bulky component to detect a paper supply "low" condition, which additional bulky component necessarily increases "footprint" and height of the printer.
Therefore, there has been a long-felt need to provide a suitable printer and receiver supply tray adapted to sense amount of receiver therein, and method thereof.